The invention relates in general to harnesses for carrying stretchers, and in particular to a harness that is capable of shifting the load to different portions of the carrier's body.
Stretchers for injured, sick, or otherwise incapacitated individuals are currently carried in the hands. Two or four people usually carry the stretcher. If two people carry the stretcher, both individuals use both hands and each carrier must bear 1/2 of the load. If four people carry the stretcher, each use only one hand and each person bears 1/4 of the total load. Carriage times are very short because the carriers must rest often, or other people must assist in the carriage. When carrying by hand, the carriers are using the small muscle groups of the hands and arms which fatigue rapidly.
There have been two groups in the medical and ergonomic literature who have attempted to improve stretcher carriage in the past. The first group was Lind and McNicol (See Lind, A. R. and McNicol, G. W., "Cardiovascular Responses to Holding and Carrying Weights By Hand and By Shoulder Harness", Journal of Applied Physiology, Volume 25, Number 3, Sep. 1968, United States, pp 261-267) who demonstrated that time to fatigue could be considerably extended when using a shoulder harness to carry a litter as opposed to hand carriage. During hand carriage, blood pressure and heart rate rose progressively until fatigue ensued in an average of about 3 minutes. With the shoulder harness, only small changes in cardiovascular measures were noted and individuals were often able to continue for the 15 minute limit of the study. Lind and McNicol did not provide a description of the type of harness used.
The second group was Rice et al (See V. Rice, "A Usability Assessment of Two Harnesses for Stretcher-Carrying," Advances in Industrial Ergonomics and Safety IV, Edited by S. Kumar, Taylor & Francis, 1992, pp 1269-1274; V. Rice, M. Sharp, W. Tharion, T. Williamson, "The Effects of Gender, Team Size, and a Shoulder Harness on a Stretcher-Carry Task and Post-Carry Performance," International Journal of Industrial Ergonomics, 18 (1996) pp 27-49) who confirmed and extended the findings of Lind and McNicol. Longer times to fatigue were achieved when men and women carried a weighted manikin (about 80 kg) using two specially designed and well described litters. Carriage times were 23 minutes with the harness and six minutes with hand carriage; however, carriage times were limited to 30 minutes so "true" times to exhaustion were not obtained. The harness used by Rice et al was designed to move the load from the hands and arms to the shoulders. The carrier's subjective reports of pain, soreness, and discomfort (PSD) suggest this was successfull: with hand carriage subjects reported more PSI) in the hands and forearm, while with the shoulder harness more PSD was reported in the neck, shoulders, chest, upper back, thighs and calves.
The present invention improves on the shoulder harness described by Rice et al. One improvement is a well padded hip belt. The hip belt allows transferring of the load from the shoulders to the hips. Proper tightening of the hip belt places the load on the top of the hips and vertical displacement allows the load to be carried on the lower body. The lower body contains most of the muscle mass in the body so that the load is distributed over a large amount of muscle tissue compared to carriage by the hands or a shoulder harness alone.
Another improvement is providing for load shifting. This is accomplished by providing the carrier with easy to reach adjustments (buckles, clips, straps and the like) which allow the carrier to transfer the load to different body parts at different times. When the hip belt is tightened and shoulder straps loosened, the load is placed on the hips. By loosening the hip belt and tightening the shoulder straps the load can be placed on the shoulders. By pulling on the horizontal shoulder strap connector the load can be shifted to different parts of the shoulders. The load can also be carried in the hands since the carrier can reach down between the two loops on either side and grasp the handles of the stretcher. Load shift should improve load carriage time because a formerly loaded muscle group can now rest and thus replenish energy and allow a return of blood flow to muscular and cutaneous areas which had previously experienced pressure.